There is a lot of visual media on youtube. It is not a very long or difficult procedure, not an all day thing. It is probably better to watch someone doing it before attempting your first square. If you want to get crazy accurate, you'll need a small metrology set up. But a reasonably straight edge and pencil line will get you something that I think will be useful out of the old tool and worth the modest effort to bring an heirloom back into service. Hopefully no one gets upset by what I just said.